1. Field of the Invention
The present invention relates to a semiconductor wafer treating apparatus and, more in particular, a semiconductor wafer treating apparatus for transferring semiconductor wafers which are stored within a cassette to a vertical type heat treatment furnace and transferring semiconductor wafers which are treated within the heat treatment furnace to the interior of the cassette.
2. Description of the Related Art
In the manufacture of semiconductor devices such as ICs, wafers are subjected to a greater number of heat treatment steps, such as an impurity diffusion, thermal oxidation, CVD (chemical vapor deposition) step, etc., in which case a heat treatment furnace is employed. A plurality of semiconductor wafers to be heat treated are arranged erect on a wafer boat made of quartz and then loaded into the heat treatment furnace.
As set out above, it is necessary to conduct various steps for the heat treatment of semiconductor wafers, such as a step for arranging semiconductor wafers which are stored in the cassette onto a wafer boat in an "erect" fashion, a step for loading the semiconductor wafers which are arranged erect on the wafer boat into the heat treatment furnace and unloading treated wafers out of the heat treatment furnace and a step for storing the treated wafers from the wafer boat into the cassette. In order to perform these steps automatically, use is made of a wafer treating apparatus for automatically transferring semiconductor wafers.
Conventionally use has been made, as a heat treatment furnace, of a lateral type as opposed to a vertical type heat treatment furnace. Recently the vertical type heat treatment furnace has been employed, mainly because it can save a considerable amount of installation area in a clean room compared with the lateral type heat treatment furnace. Further, the vertical type heat treatment furnace provides a following additional advantage. In the case where the lateral type furnace is used, the wafer boat is likely to contact the inner wall of the process tube in the furnace when it is introduced into the process tube. Therefore, precise control is required for attaining soft-landing in which the wafer boat is introduced into the process tube while being kept separate from the inner wall. However, in the case where the vertical type heat treatment furnace is used, the soft-landing can be easily attained by merely elevating the wafer boat within the vertical process tube.
In the vertical type furnace, semiconductor wafers to be treated are loaded into the furnace, while being transferred in a vertical as opposed to a horizontal direction. To this end, a different wafer transfer apparatus is required upon comparison with the transverse furnace.
In the case of the vertical type furnace, there is a tendency for a plurality of such furnaces to be employed in a single manufacturing line in view of the merits of the vertical type furnace, such as the smaller installation area required. Effective equipment is, therefore, required to allow the to-be-treated semiconductor wafers to be effectively transferred to and from the plurality of vertical type furnaces.